Method for treating water contaminated with methanol and boron

ABSTRACT

Systems and methods have been developed for treating the waste water contaminated with methanol and boron in addition to other contaminants. The systems and methods allow specifically for the removal of the methanol and boron without the addition of significant chemicals to raise the pH. The water is treated by removing the methanol via biological digestion in a bioreactor, separating a majority of the contaminants from the water by reverse osmosis and removing the boron that passes through the reverse osmosis system with a boron-removing ion exchange resin.

RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.60/767,574, filed Sep. 1, 2006, which application is hereby incorporatedherein by reference.

BACKGROUND

Water, especially in the western United States and other arid regions,is a valuable resource. Many oil and natural gas production operationsgenerate, in addition to the desired hydrocarbon products, largequantities of waste water, referred to as “produced water”. Producedwater is typically contaminated with significant concentrations ofchemicals and substances requiring that it be disposed of or treatedbefore it can be reused or discharged to the environment. Produced waterincludes natural contaminants that come from the subsurface environment,such as hydrocarbons from the oil- or gas-bearing strata and inorganicsalts. Produced water may also include man-made contaminants, such asdrilling mud, “frac flow back water” that includes spent fracturingfluids including polymers and inorganic cross-linking agents, polymerbreaking agents, friction reduction chemicals, and artificiallubricants. These contaminants are injected into the wells as part ofthe drilling and production processes and recovered as contaminants inthe produced water.

Commonly encountered non-natural contaminants in produced water, andtheir sources, are discussed below.

From high-viscosity fracturing operations—gellants in the form ofpolymers with hydroxyl groups, such as guar gum or modified guar-basedpolymers; cross-linking agents including borate-based cross-linkers;non-emulsifiers; and sulfate-based gel breakers in the form of oxidizingagents such as ammonium persulfate.

From drilling fluid treatments—acids and caustics such as soda ash,calcium carbonate, sodium hydroxide and magnesium hydroxide;bactericides; defoamers; emulsifiers; filtrate reducers; shale controlinhibitors; deicers including methanol and thinners and dispersants.

From slickwater fracturing operations—viscosity reducing agents such aspolymers of acrylamide.

Because of the very wide range of contaminant species as well as thedifferent quality of produced water from different sources, efforts tocreate a cost effective treatment system that can treat or recycle thespectrum of possible produced water streams have little success. Forexample, while reverse osmosis is effective in treating many of theexpected contaminants in produced water, it is not very effective inremoving methanol and it may be fouled by even trace amounts ofarcylamide.

As another example, there have been many attempts to reclaim producedwater and reuse it as fracturing feed water, commonly referred to as“frac water.” Frac water is a term that refers to water suitable for usein the creation of fracturing (frac) gels which are used in hydraulicfracturing operations. Frac gels are created by combining frac waterwith a polymer, such as guar gum, and in some applications across-linker, typically borate-based, to form a fluid that gels uponhydration of the polymer. Several chemical additives generally will beadded to the frac gel to form a treatment fluid specifically designedfor the anticipated wellbore, reservoir and operating conditions.

However, some waste water streams are unsuitable for use as frac waterin that they require excessive amounts of polymer or more to generatethe high-viscosity frac gel. For example, trace amounts of spentfriction reducers in the stream inhibit the added polymer from gelling.Because it can be difficult to prevent produced water streams fromdifferent sources from being co-mingled, this typically results in allproduced water from a well field being made unsuitable for recycling asfrac water.

An additional problem occurs when the produced water is alsocontaminated with methanol and it is desirable to discharge the water tothe environment. One way to treat produced water to the extent necessaryto discharge the water to the environment, is through filtrationtechniques such as ultra filtration and reverse osmosis. However,methanol will pass through nearly any available membrane filtrationtechnology.

Yet another problem occurs when the produced water is also contaminatedwith boron, such as from the use of borate-based cross-linking agents,and it is desirable to discharge the water to the environment. One wayto treat produced water with boron is referred to as the HERO process inwhich the pH is raised up to at least about 11 prior to treatment withreverse osmosis, resulting in the boron being rejected with the reverseosmosis reject brine. However raising the pH has several undesirableattributes. First, there is increased scaling within the reverse osmosissystem increasing the maintenance costs of the system. Second, the pHmust then be reduced before the treated water may be discharged to theenvironment. Third, the cost of the chemicals to raise the pH coupledwith the cost of immediately thereafter lowering the pH and the cost ofdisposal of the precipitated salts resulting from the lowering of the pHmake the HERO process very expensive.

SUMMARY

Systems and methods have been developed for reclaiming watercontaminated with the expected range of contaminants typicallyassociated with produced water, including water contaminated with slickwater, methanol and boron. A pretreatment system is effective inproducing a stream of water that is primarily contaminated with methanoland boron. This disclosure further describes systems and methods fortreating the pretreated water specifically for the removal of themethanol and boron without the addition of significant chemicals toraise the pH. The water is treated by removing the methanol viabiological digestion in a bioreactor, separating a majority of thecontaminants from the water by reverse osmosis and removing the boronthat passes through the reverse osmosis system with a boron-removing ionexchange resin.

In part, this disclosure describes a method for treating a watercontaining contaminates including methanol and boron. The methodincludes biologically digesting the water, thereby reducing theconcentration of methanol in the water. The method further includesseparating contaminants from the water using reverse osmosis, althoughthe reverse osmosis passes an undesirable amount of the boron in itspermeate. Subsequently the method removes the boron from the reverseosmosis permeate via a boron-selective removal process.

In part, this disclosure describes a system for removing contaminantsfrom a stream of produced water containing varying concentrations ofcontaminates including boron derived from borate crosslinkers. Thesystem includes a reverse osmosis system that treats the stream andremoves contaminants passing at least some boron in its permeate; and aboron-selective resin system that removes boron from the reverse osmosispermeate.

In part, the disclosure further describes a system for treating watercontaminated with methanol and boron. The system includes at least onebioreactor that biologically digests methanol in the water until adesired concentration of methanol is obtained; a boron-selective removalsystem that removes boron from the water until a desired concentrationof boron is obtained; and at least one filtration system that removescontaminants from the water until a desired concentration ofcontaminants other than boron and methanol is obtained.

These and various other features as well as advantages will be apparentfrom a reading of the following detailed description and a review of theassociated drawings. Additional features are set forth in thedescription which follows, and in part will be apparent from thedescription, or may be learned by practice of the described embodiments.The benefits and features will be realized and attained by the structureparticularly pointed out in the written description and claims hereof aswell as the appended drawings.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and areintended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The following drawing figures, which form a part of this application,are illustrative of embodiments systems and methods described below andare not meant to limit the scope of the invention in any manner, whichscope shall be based on the claims appended hereto.

FIG. 1 illustrates an embodiment of a system for treating contaminatedwater.

DETAILED DESCRIPTION

Unless otherwise indicated, all numbers expressing quantities ofingredients, properties such as molecular weight, concentrations,reaction conditions, temperatures, and so forth used in thespecification and claims are to be understood as being modified in allinstances by the term “about.” Accordingly, unless indicated to thecontrary, the numerical parameters set forth in the followingspecification and attached claims are approximations that may varydepending upon the desired properties sought to be obtained. At the veryleast, and not as an attempt to limit the application of the doctrine ofequivalents to the scope of the claims, each numerical parameter shouldat least be construed in the light of the number of reported significantdigits and by applying ordinary rounding techniques.

The term “residence time” refers to the average length of time that afluid or particle spends within a process vessel or in contact with acatalyst. For the purposes of this discussion, the mean residence timeof a vessel is defined by dividing the volume of liquid in a vessel(e.g., volume in cubic feet) by the volumetric flow rate of the liquid(e.g., in cubic feet per second).

The term “floating” as used herein refer to treating a liquid with aflotation operation to separate solid or liquid particles from a liquidphase. There are several types of flotation operations that are wellknown in the art including dissolved-air flotation (DAF), air flotationand vacuum flotation.

Fracturing gel or “frac gel” refers to a high-viscosity gel fluid mixfor use in fracturing a subterranean formation. The term “fracturinggel” will be used herein to refer to a fluid having a viscosity greaterthan about 100 centipoise when injected into the subsurface for thepurpose of fracturing the subsurface formations. The term “Fracturingwater,” as discussed above, refers to the water to which the gellant isadded in order to create the fracturing gel. For the purposes of thisdisclosure, however, a water is suitable for use as fracturing water ifit can be mixed with an economical amount of guar gum, relative to otherclean water supplies, to create a frac gel. That is, a water is notsuitable for use as fracturing water if it requires significantly morepolymer (in order to achieve target properties of the frac gel) thanother sources of water readily available. Thus, for the purposes of thisdisclosure, a water is considered suitable for use as fracturing wateronly if it can be mixed with an amount of polymer (e.g., guar gum, guargum derivatives, or other commonly applied gelling agent in thefracturing industry, that will create a frac gel) to create a frac gelhaving a stable viscosity greater than about 50 centipoise at theinjection temperature, and the amount of gelling agent required is nomore than about 10% greater than that amount required to create the sameviscosity using an equivalently salty water, i.e., distilled water mixedwith an equivalent amount of salt content as the purported fracturingwater.

Slick water, on the other hand, refers to a relatively low viscosityaqueous fluid used also for fracturing a subterranean formation. Theterm “slick water” as used herein further refers to low viscosity (i.e.,a viscosity less than that used for frac gels) fluid to which frictionreduction agents have been added to modify the flow characteristics ofthe fluid. For example, slick water is often created by adding a smallamount of polymer to water in order to change the flow characteristicsof the resulting aqueous mixture. Such friction reduction agentsinclude, but are not limited to, polyvinyl polymers,polymethacrylamides, cellulose ethers, polysaccharides, lignosulfonates,and ammonium, alkali metal, and alkaline earth salts thereof. Specificexamples of typical water soluble polymers are acrylic acid-acrylamidecopolymers, acrylic acid-methacrylamide copolymers, polyacrylamides,partially hydrolyzed polyacrylamides, partially hydrolyzedpolymethacrylamides, polyvinyl alcohol, polyvinly acetate,polyalkyleneoxides, carboxycelluloses, carboxyalkylhydroxyethylcelluloses, hydroxyethylcellulose, galactomannans (e.g., guar gum),substituted galactomannans (e.g., hydroxypropyl guar, carboxymethylhydroxypropyl guar, and carboxymethyl guar), heteropolysaccharidesobtained by the fermentation of starch-derived sugar (e.g., xanthangum), and ammonium and alkali metal salts thereof. Preferredwater-soluble polymers include hydroxyethyl cellulose, starch,scleroglucan, galactomannans, and substituted galactomannans. Forexample, copolymers of acrylamides are disclosed as good frictionreduces in U.S. Pat. No. 3,254,719 and U.S. Pat. No. 4,152,274, whichdisclosures are hereby incorporated herein by reference. An example ofan acrylamide-based friction reducer includes that sold under theproduct name FRW-14 by BJ SERVICES COMPANY. Others are well known in theart.

It should be noted that both fracturing fluids and slick water mayinclude other compounds such as demulsifiers, corrosion inhibitors,friction reducers, clay stabilizers, scale inhibitors, biocides, breakeraids, mutual solvents, alcohols, surfactants, anti-foam agents,defoamers, viscosity stabilizers, iron control agents, diverters,emulsifiers, foamers, oxygen scavengers, pH control agents, and buffers,and the like.

When referring to concentrations of contaminants in water or to waterproperties such as pH and viscosity, unless otherwise stated theconcentration refers to the concentration of a sample properly taken andanalyzed according to standard Environmental Protection Agency (EPA)procedures using the appropriate standard test method or, where noapproved method is available, commonly accepted methods may be used. Forexample, for Oil and Grease the test method identified as 1664A is anapproved method. In the event two or more accepted methods provideresults that indicate two different conditions as described herein, thecondition should be considered to have been met (e.g., a condition thatmust be “above pH of about 7.0” and one accepted method results a pH of6.5 and another in pH of 7.2, the water should be considered to bewithin the definition of “about 7.0”).

FIG. 1 illustrates an embodiment of a system for treating contaminatedwater. The contaminated water may be produced water 120 generated by oilfield operations or waste water from some other industrial orresidential source. The system 100 is illustrated and discussed below asa continuous flow system. However, in an alternative embodiment some orall of the processes of the system 100 may be operated as batchprocesses.

In the embodiment shown, the contaminated water is produced water 120generated from oil, gas or other subsurface extraction operations. In anembodiment, the produced water is contaminated with methanol and boronderived either from natural sources in the subsurface or added as partof the extraction operations.

In an embodiment, the system of FIG. 1 is anticipated to receiveproduced water having at least about 7,000 milligrams per liter (mg/l)of total dissolved solids (TDS), at least about 10 mg/l of boron, and atleast about 500 mg/l methanol, although the system could be used totreat less contaminated water as well. Furthermore, as discussed ingreater detail below, the effluent of the system 100 is desired tocontain less than about 500 mg/l of TDS, less than about 2 mg/l boron,and less than about 1 mg/l methanol. Preferably, the system 100 canaccept any produced water of any quality. In testing, waste water,including produced water with the following ranges of contaminant asprovided in Table 1 concentrations, were treated.

TABLE 1 Parameter Range TDS @ 180 C., mg/l up to at least 8830 TSS @ 105C., mg/l up to at least 141 Turbidity, NTU up to at least 239 TOC, mg/lup to at least 1130 COD, mg/l up to at least 5750 BOD, mg/l up to atleast 1820 pH up to at least 7.21 Iron, mg/l up to at least 0.3Chloride, mg/l up to at least 4310 Potassium, mg/l up to at least 59.2Calcium, mg/l up to at least 78.5 Magnesium, mg/l up to at least 9.1Sodium, mg/l up to at least 2750 Sulfate, mg/l up to at least 26Carbonate, mg/l ND as CO₃ Bicarbonate, mg/l up to at least 459 as HCO₃Boron, mg/l up to at least 11.6 Methanol, mg/l up to at least 610

In an embodiment, the produced water 120 may also be contaminated withslick water and thus may contain friction reducers such as acrylamides.Such contaminants are relevant in that they are hard to remove, foulmany treatment operations such as reverse osmosis systems, and inhibitthe formation of fracturing gels if the contaminant exists in sufficientconcentration in fracturing water.

The system 100 is designed in anticipation that the produced water 120is likely to contain these contaminants at all times or intermittently.

The system 100 receives the produced water 120 and may temporarily storeit, such as in a holding tank, before beginning active treatment. Theproduced water 120 may be received via truck, pipeline, surface flow orany other suitable method. Produced waters 120 from different sourcesmay also be received and co-mingled immediately or independently treateduntil the anaerobic treatment stage discussed below. As the system isadapted to treat any type of expected contaminant, this is an advantageover other systems that are tailored to specific water qualities fromspecific wells or sources.

The produced water 120 may be treated with a gravity separator, such asan API separator as shown, to remove immiscible phases of oil andgrease. Gravity separation is well known and any suitable gravityseparation system, e.g., API separator design, gunbarrel separator orgravity clarifier, may be used.

The aqueous separator effluent 122 then is transferred to the anaerobictreatment system 104 for anaerobic digestion of contaminants. In anembodiment, an anaerobic pond may be used as the anaerobic treatmentsystem or as part of the anaerobic treatment system 104. Anaerobic pondsare known in the art and refer to a deep pond that maintains anaerobicconditions at depth, except for a shallow (typically less than about 2feet) surface zone. In an embodiment, some oxygen may be added to watercontained in the anaerobic pond through spray evaporation and ambientcontact with air, as long as very little dissolved oxygen is achievedbelow 2 feet of depth to ensure that the conditions at depth remainanaerobic. In an embodiment, other than mixing incidental to the mixingof the effluent 112 with the contents of the anaerobic treatment system104 vessel, no additional mixing or aeration is provided by theoperators.

The anaerobic treatment system 104 treats the water by anaerobicconversion of organic wastes into carbon dioxide, methane, other gaseousend products, alcohols possibly including methanol, and organic acids.Inorganic wastes may also be anaerobically converted. Some separationwill occur in the anaerobic treatment system 104 due to precipitation ofconverted contaminants as well as via settling. In operation, it wasnoted that anaerobic digestion served at least two beneficial purposes.First, it typically reduced chemical oxygen demand (COD) by 30% or moreand usually by at least 50%. However, it notably did not reducebiological oxygen demand (BOD) by very much. Second, anaerobic digestionreduced the ratio of COD to BOD from the initial value (typically around3:1) to 2:1 or less.

In an embodiment, the water is treated in the anaerobic treatment system104 based on residence time. A mean residence time of at least about 50days has been found to be effective. Larger mean residence times arealso effective. In an alternative embodiment, an alternative benchmarkor combination of benchmarks may be used to determine if sufficienttreatment has occurred, such as a targeted COD reduction relative to theinlet amount (e.g., at least about 15% reduction, or at least about 30%or at least about 50% reduction criteria) or threshold COD to BOD ratiobeing achieved. A combination benchmark may include a minimum of 50 daysresidence time and any other benchmark such as COD concentration.

Effluent 124 from the anaerobic treatment system 104 is transferred toan aeration system 106, which may also be referred to as an aerator 106.The aeration system 106 actively aerates the water to allow thebiological digestion of contaminants in the water over time. In anembodiment, the aeration system 106 treats the water for a meanresidence time of at least about 5 days with mean residence times of 5to 10 days being one treatment target. During treatment, the dissolvedoxygen of the system is monitored and the aeration is adjusted tomaintain a dissolved oxygen concentration above at least 50% of thesolubility limit of oxygen in water at the aeration system 106temperature, preferable above 75% of the solubility limit and morepreferable above 90% of the solubility limit. However, the targetdissolved oxygen concentration used may be balanced against the cost ofproviding the aeration and current throughput needs of the system.

In an embodiment, no supplemental nutrients for bioremediation are addedin the aeration treatment step. The amount of aeration may be controlledbased on measurement of dissolved oxygen of the water in the aerationsystem 106. Aeration may also be controlled based on the effectivenessof the flotation treatment and water quality of the flotation treatmenteffluent 128. Submerged combustion heaters, or other heat sources, maybe used to raise water temperature as desired, such as in the winter toprevent water freezing if the aerator 106 is an outdoor pond.

In addition to biological digestion, it is believed that some oxidationor other aerobic conversion of some contaminants occurs in the aerationsystem 106. In an embodiment, a benchmarks to determine proper aerationmay include a minimum residence time at a specific rate of aeration andtemperature, a reduction of BOD to below a target threshold (e.g., lessthan about 1300 mg/l, or more preferably less than about 1000 mg/l), areduction of sulfate to below 10 mg/l sulfate, a reduction of 50-75% ofthe input concentration of sulfate in the anaerobic treatment systemeffluent 124, and/or a reduction in barium to less than 1 mg/l. However,as mentioned above, sufficient aeration is primarily indicated by theeffectiveness of the flotation treatment and water quality of theflotation treatment effluent 128.

In the aeration system 106, aerobic digestion of trace metals occurshelping to clarify these compounds and serves many beneficial functions.First, aerobic digestion of trace metals occurs helping to clarify thesecompounds. This was evidenced by analyses of sludge taken withinsufficient aeration and sufficient aeration showing that insufficientaeration resulted in leachable barium (determined by the TCLP analysis)being found in the sludge whereas, under conditions of proper aeration,leachable barium was reduced below the detection limit.

Experimental data suggest that the aeration step does reduce the COD andBOD of the water being treated, but, without being bound to anyparticular theory, the aeration step also appears to cause a change inthe nature of the COD which increases the effectiveness of the flotationsystem 108 in removing contaminants. This was evidenced by experimentsin which insufficiently aerated effluent from the aeration system 106was transmitted to the flotation system 108 and it was found that theflotation system's ability to coagulate and separate contaminants wasdrastically reduced. Notably, another effect of insufficient aerationobserved during testing was that the resulting COD that was passed bythe DAF 108 fouled the bioreactor 112. Proper aeration eliminated thisfouling. Without being limited to a particular theory, it is believedthat the COD in produced water contaminated with frac flow back water isat least in part due to long chain acrylamide polymers, fragments offrac gel and other stimulation chemicals, that can be floated out in theDAF, but only after conversion by the digestion operations 104, 106.

In an embodiment, an aeration pond is used as the aeration system 106.Aeration ponds are known in the art. An aeration pond is typically alarge, shallow earthen basin provided with some means for activelyaerating the water contained in the pond. Types of active aeration usingair include sprayers that spray the water into the air and forced airinjection via diffusers submerged in the pond attached to floatingaerators. Many other aeration means are known in the art; any suitablemeans for aerating the water may be used.

Aeration system effluent 126 is transferred, with heat as needed forproper operation, to a flotation separator 108. The flotation separator108 separates solid particles from the aqueous phase by introducing finegas bubbles into the aqueous phase. The bubbles attach to theparticulate matter and the buoyant force of the combination is greatenough cause the particle to rise to the surface and subsequently beskimmed off or otherwise mechanically separated from the aqueous phase.

Flotation separators 108 are well known in the art. In experiments, adissolved air flotation (DAF) separator was used to float and separateparticulates from the aqueous phase, however there is no reason tobelieve that other flotation separators, such as air flotation or vacuumflotation systems, may not also be effective. In embodiments thatutilize a DAF separator, any suitable DAF design, now known or laterdeveloped may be utilized. For example, a three vessel DAF in whichcoagulant is added in the first vessel, the flocculant is added in thesecond vessel and the third vessel is the actual flotation chamber inwhich air is added and separation occurs.

Furthermore, any DAF additives may be used as determined to beexperimentally suitable in increasing the effectiveness of the DAFseparator in removing contaminants. Commercially available coagulantswere used to assist the coagulation and increase the performance of theDAF. In an embodiment, Ashland Chargepac 55 with a dose rate between 100and 200 ppm was used as the coagulant and flocculant polymer was mixedfrom Ciba Magnafloc 336 and then diluted to a final dose rate of 2 to7.5 ppm. Preferably, the DAF separator is operated above 35 degrees F.and more preferably at about 55 degrees F. In an embodiment, the DAFseparator is operated as necessary to obtain an effluent 128 with an NTUlevel of less than about 10 NTU.

In the embodiment shown, the aqueous effluent 128 of the flotationseparator 108 is further clarified by passing the effluent 128 through afiltration system 110. Additionally, the effluent 128 may be monitored,such as via a turbidity meter, conductivity sensor or other monitoringdevice. If the observed level does not meet the desired level oftreatment, the effluent 128 may be recycled to an earlier treatmentoperation. Furthermore, at any point after the aerobic digestion, abiocide may be introduced to eliminate microbes and promote removal ofsame, such as in the DAF separator 108 or the filtration system 110 orprior to shipment to a frac system.

In the embodiment shown, a sand filter, nominally effective as a 10micron filter, was used as the filtration system 110 to achieve aturbidity of less than about 5 NTU and preferably less than about 1 NTU.Other filtration designs may also be used. Effluent 128 from the DAFseparator 108 may be feed via gravity through the filters 110 to a liftstation that transfers water to one or more intermediate surge tanks. Inorder to achieve the desired level of treatment, one or more separatefilters may be utilized in series or in parallel. In an embodiment, eachsand filter may be equipped with a sight glass to show the operator howmuch head is developing in the filter and also with an inline turbiditymeter to directly measure filter performance. When the feed water levelin the filter reaches the high tank level switch a backwash cycle may beinitiated by a programmable logic controller (PLC) that monitorsoperation of the filters or the system as whole. The back wash cycle mayalso be triggered manually or based on the readings of the turbiditymeter. Back wash water and overflow from the sand filter inlet may berecycled to any prior treatment operation as desired by the operator.

The effluent 130, 132 of the filtration system 110 is suitable for useas a fracturing water even though in experiments it still containedsignificant concentrations of COD, total organic carbon (TOC), TDS, andbiological oxygen demand (BOD). Its use as a fracturing water wasevidenced by the ability to gel sufficiently when combined with polymersto create a high-viscosity fracturing gel. Without being bound to aparticular theory, it is believed that trace amounts of the frictionreducers from slick water impair the gelling reaction. These frictionreducers are also very difficult to remove using either anaerobic oraerobic treatment alone and also difficult to remove without the use offlotation. Indeed, it is believed the combination of anaerobic, aerobicand flotation treatment operations is the most effective way ofreclaiming produced water that is unsuitable for use as fracturing waterand convert it into water that is suitable for use as a fracturingwater.

Typical and target values of contaminant concentrations for fracturingwater 130, 132 obtained from the system 100 are provided below in Table2.

TABLE 2 Parameter Range Target TDS @ 180 C., mg/l  9,000-16,000 <10,000TSS @ 105 C., mg/l  0-100 <75 Turbidity, NTU 0-5 <1 TOC, mg/l 400-800<700 COD, mg/l 1000-3000 <2000 BOD, mg/l  500-1500 <1000 pH 6.5-8  7-7.5 Iron, mg/l  1-10 <5 Chloride, mg/l  5,000-10,000 <6,000 Potassium,mg/l 100-500 <300 Calcium, mg/l  50-250 <150 Magnesium, mg/l  10-100 <25Sodium, mg/l 2000-5000 <3000 Sulfate, mg/l  40-200 <50 Carbonate, mg/l 0-100 <25 Bicarbonate, mg/l  100-1200 <800 Boron, mg/l  0-20 <15

In the embodiment shown in FIG. 1, in addition to generating watersuitable for reuse as fracturing water, additional treatment operationsare provided that treat the produced water to a quality sufficientlyclean for discharge to the environment. Thus, the depending on the needfor frac water, the system 100 may be operated so that more or less fracwater 130 is produced from the produced water 120 stream. Any surplus ofunused frac water 130 may then be treated by the remaining portions ofthe system 100 to a water quality that allows the water to be dischargedto the environment.

Treatment of the frac water 130, 132 to a quality suitable for dischargeto the environment requires that the system 100 address methanol andboron concentrations. Methanol is often a contaminant in produced water.In addition, anaerobic digestion may produce methanol from the digestionof guar gels. Testing has shown that in the system shown in FIG. 1 whilesome methanol reduction (e.g., at the top of the pond) may occur undercertain conditions during the anaerobic treatment operation, methanolmay be treated significantly during the aeration treatment. However, theaeration system 106 as described can not be depended to sufficientlytreat all of the methanol in the produced water. This variability may bedue to lack of nutrients, composition of the particular inlet producedwater being treated or the ambient weather conditions under which theaeration treatment is being.

In the embodiment shown, the system 100 further provides for theeffluent 132 of the filtration operation to be transferred to one ormore bioreactors 112, 114 for the biological digestion of the effluent132. Biological digestion of the effluent 132 drastically reduces theconcentration of the methanol in the water. In an embodiment, thebiological digestion of the effluent 132 is performed for a durationsufficient to reduce the methanol to below the target discharge limit oralternatively to a level at which the methanol can no longer bedetected.

In the embodiment shown, two stages of biological digestion areperformed. First, a bioreactor 112 may be used to perform the majorityof the biological digestion. In an embodiment, the bioreactor may be anenclosed vessel, such as a steel tank with internal epoxy coating andstandard tank roof with appropriate vents. Coarse bubble diffusers maybe mounted on the bottom of the tank with air supplied by compressors.The bioreactor 112 may or may not be heated as needed to maintain ahealthy biological environment for digestion. Additionally, nutrientsmay be added, such as gaseous ammonia for nitrogen and phosphoric acidfor phosphorous, as necessary. In an embodiment, a residence time may bechosen so that methanol is completely eliminated or reduced to a desiredconcentration in the bioreactor 112. The design and operation ofbioreactors are well known in the art and any suitable design may beutilized as part of this operation.

In the embodiment shown, a second, and optional, stage of combinedbiological digestion and filtration is provided in which the effluent134 of the bioreactor 112 is transferred to a membrane bioreactor (MBR)114 as shown. The MBR 114 provides additional biological digestion aswell as removing by filtration some contaminants contributing to TOCconcentrations in the water 134. Cleaned water (permeate 136) isextracted through the membranes of the MBR 134. In an embodiment, rejectfrom the MBR 114 may be returned to the bioreactor 112 for additionaldigestion or to any other prior treatment stage. Any suitable membranebioreactor design may be utilized, for example a hollow fiber membranebioreactor such as that sold by ZENON under the trademark ZEEWEED issuitable for use as the MBR 114.

Permeate 136 of the MBR 114 is transferred to an RO system. In theembodiment shown, a reverse osmosis (RO) system 116 is used to filterthe remaining TOC, TDS and other contaminants from the permeate 136 to alevel acceptable for discharge, except boron. RO systems 116 are wellknown in the art and any design, now known or later developed, may beutilized.

Notably, where the pH of the water is not raised, such as for thepurposes of precipitating out contaminants, in the prior operations suchas is necessary in the HERO process. In an embodiment, there may be someminor reduction of pH in order to maintain the proper conditions withinthe bioreactor. This, however, does not cause the precipitation of anycontaminants, but rather increases the solubility of some contaminants.The pH of the RO permeate 138 will be dictated primarily by the pH ofthe produced water 120. Thus, the pH of the RO permeate 138 willgenerally be much lower than the permeate of the RO in a HERO process.Preferably the RO permeate 138 in the system 100 will be less than about10.0, still yet less than about 9.0 and even more advantageously lessthan about 8.0 and greater than about 6.5.

By avoiding lime softening, the production of waste solids by the system100 is significantly lower in comparison. Other than solids derived fromthe original contaminants in the produced water feed, the major sourceof solids generated as a result of the treatment operations is due theuse of liquid coagulant in the DAF. This represents a significant costsavings over systems and processes that actively adjust the pH throughchemical addition as part of the treatment.

However, because of the pH range at which the RO 116 is operated asdescribed above, boron will not be removed from the water by the ROsystem 116 in quantities sufficient to meet the desired dischargeconcentration. In experimental analyses, MBR effluent 136 containedroughly the same concentration of boron as the produced water 120. TheRO system 116 is expected to pass a significant portion of the boron inthe stream—a portion that is expected to be beyond the limits necessaryto discharge the boron to the environment.

In the system 100 of FIG. 1, boron is removed from the RO permeate 138by means of a boron-selective treatment system 118. In an embodiment,the boron selective treatment system 118 is an ion-exchange resinadapted to optimally remove boron from an otherwise relatively cleanaqueous stream. One example of such a resin suitable for use in thesystems described herein is that offered by Dow Chemical under the tradename of XUS-43594.00, now alternately referred to under the trade nameBSR1, which is marketed as a uniform particle size weak base anionexchange resin for selective boron removal. Other boron-selected resinsknown in the art include the product MK-51 sold by SYBRON and S-108 soldby PUROLITE. Other systems that are effective for removing boron mayalso be used, whether now known or later developed. In fact, because theRO permeate 138 is substantially clean except for the boron, anyeffective boron removal system may be used without worry of fouling ordegradation due to other contaminants.

Effluent 140 of the boron-selective treatment system 118 will be ofsufficient quality to be discharged to the environment. Exemplifiedtarget values of contaminant concentrations for effluent 140 from anembodiment of the system 100 are provided below in Table 3. If, upontesting, the values are outside of the target ranges, the effluent 140may be recycled to one of the treatment operations until the effluent140 quality meets the discharge requirements.

TABLE 3 Parameter Range TDS <500 mg/l TOC <5 mg/l Boron 1-2 mg/l pH6.5-9.0 Oil & Grease <10 mg/l Radium 226 <60 mg/l Chlorides <230 mg/l

Various waste streams other than the primary aqueous streams discussedmay be disposed in any suitable manner. For example, reject from the ROsystem 116 may be used as backwash for prior treatment systems, shippedto the oilfield for use as frac water, returned to the treatment flowfor reprocessing and further concentration or disposal via injectionwell. As a further example, in embodiments using an ion-exchange resinfor boron removal, the boron-laden regenerate from the ion-exchangeregeneration may be blended with RO reject fluid to neutralize theregenerate and injected in the disposal well.

In an embodiment, some or all of the operations of the treatment systemmay be automated used process controllers, automated transfer pumps,flow control valves, sensors and other equipment as is known in the art.

The fracturing water 130 output of the system 100 may be stored inholding tanks prior to transfer to a fracturing gel production systemvia pipeline or truck to a wellhead or other location where fracturingchemicals are added to generate fracturing gel. Similarly, theboron-selective treatment system effluent may be discharged to a holdingtank for confirmation testing prior to discharge.

Those skilled in the art will recognize that the methods and systems ofthe present disclosure may be implemented in many manners and as suchare not to be limited by the foregoing exemplary embodiments andexamples. In other words, functional elements being performed by asingle or multiple components, in various combinations. In this regard,any number of the features of the different embodiments described hereinmay be combined into single or multiple embodiments, and alternateembodiments having fewer than or more than all of the features hereindescribed are possible.

While various embodiments have been described for purposes of thisdisclosure, various changes and modifications may be made which are wellwithin the scope of the present invention. For example, between one ormore of the treatment operations described herein, transfer pumps, surgetanks, control valves, heaters, and other equipment may be provided toassist the efficient operation and maintenance of the system and toprovide for various contingencies such as surges, cleaning operations,recycling of flow, bypassing of operations, and low or high ambienttemperatures. As a specific example, water being transferred between anytwo operations may be analyzed and recycled to a previous stage ifcertain contaminant concentrations are out of a predetermined desiredrange. Additionally, if the system is operated as a continuous flowsystem, surge tanks and overflow capacity may be provided at differentpoints within the system to allow for the system throughput to managedas necessary to obtain the proper water quality at each stage oftreatment.

Numerous other changes may be made which will readily suggest themselvesto those skilled in the art and which are encompassed in the spirit ofthe invention disclosed and as defined in the appended claims.

1. A method for treating a water containing contaminants, thecontaminants including methanol and dissolved solids including boron,comprising: biologically digesting the water, thereby reducing theconcentration of methanol in the water; separating contaminants from thewater using reverse osmosis, the reverse osmosis passing an undesirableamount of the boron but an acceptable amount of other dissolved solidsin its permeate; and removing the boron from the reverse osmosispermeate via a boron-selective removal process.
 2. The method of claim 1further comprising: receiving the water at a first pH less than about10.0; and wherein the steps of biologically digesting, separating andremoving are performed on water at a pH less than about 10.0 and withoutadding chemicals to raise the pH.
 3. The method of claim 1 furthercomprising: biologically digesting the water until a desiredconcentration of methanol in the water is obtained.
 4. The method ofclaim 1 further comprising: biologically digesting the water beforeseparating the contaminants from the water using reverse osmosis.
 5. Themethod of claim 1 further comprising: removing the boron by passing thewater through an ion-exchange resin selected for the removal of boron.6. The method of claim 1 further comprising: wherein the pH of thepermeate reverse osmosis water obtained from the separating is less thanabout
 10. 7. The method of claim 6 further comprising: wherein the pH ofthe permeate reverse osmosis water obtained from the separating is lessthan about
 9. 8. The method of claim 7 further comprising: wherein thepH of the permeate reverse osmosis water obtained from the separating isless than about
 8. 9. The method of claim 1 further comprising:discharging water effluent of boron-selective removal process to theenvironment.
 10. The method of claim 1 wherein biologically digestingthe water further comprises: digesting the water in a first aerobicbioreactor; and after digesting the water in the first aerobicbioreactor, passing the water through a membrane bioreactor that bothfilters and aerobically digests the water from the first bioreactor. 11.The method of claim 2 wherein the first pH is less than about 8.0.
 12. Amethod for treating a water containing contaminates, the contaminantsincluding an initial concentration of methanol and an initialconcentration of inorganic salt including boron, comprising:biologically digesting the water, thereby reducing the concentration ofmethanol in the water; passing the water through a desalination processto obtain a first amount of water having a concentration of inorganicsalt less than the initial concentration of inorganic salt; receivingthe water at a first pH less than about 10.0; and wherein the steps ofbiologically digesting and passing are performed on water at a pH lessthan about 10.0.
 13. The method of claim 12, wherein passing the waterthrough a desalination process further comprises: obtaining a secondamount of water having a concentration of inorganic salt greater thanthe initial concentration of inorganic salt.
 14. The method of claim 13,wherein the desalination process includes a reverse osmosis system, thefirst amount of water being reverse osmosis permeate and the secondamount of water being reverse osmosis reject.
 15. The method of claim14, wherein the pH of the reverse osmosis permeate obtained from thepassing operation is less than about 10.0.
 16. The method of claim 14,wherein the pH of the reverse osmosis permeate obtained from the passingoperation is less than about 9.0.
 17. The method of claim 14, whereinthe pH of the reverse osmosis permeate obtained from the passingoperation is less than about 8.0.
 18. The method of claim 12 whereinbiologically digesting the water further comprises: digesting the waterin a first bioreactor; and after digesting the water in a firstbioreactor, passing the water through a membrane bioreactor that bothfilters and digests the water from the first bioreactor.
 19. The methodof claim 12 wherein the first pH is less than about 8.0.
 20. The methodof claim 12 further comprising: biologically digesting the water until adesired concentration of methanol in the water less than the initialconcentration of methanol is obtained.
 21. The method of claim 12wherein biologically digesting the water comprises: passing the waterthrough a membrane bioreactor that both filters and digests the water.22. The method of claim 14 wherein the inorganic salt includes at leastone salt of boron and where the reverse osmosis permeate contains anundesirable amount of boron, the method further comprising: removingboron from the reverse osmosis permeate via a boron-selective removalprocess.